Back to EveryPatent.com
| United States Patent |
5,625,227
|
|
Estes
, et al.
|
April 29, 1997
|
Circuit board-mounted IC package cooling apparatus
Abstract
In a circuit board/IC package assembly the die cavity in the IC package
body portion is filled with a thermally conductive liquid to substantially
facilitate the transfer of operational die heat toward the inner, lid side
of the IC package that faces the circuit board. To dissipate the die heat
received by the die cavity lid, a spaced series of metal-plated through
holes are formed in the circuit board. The metal plating portions of the
through holes are engaged with an internal ground plane structure within
the circuit board, and are thermally coupled to the IC package die cavity
lid. Accordingly, during operation of the IC package, die heat is
conducted to the ground plane structure sequentially through the die
cavity liquid, the cavity lid, and the metal-plated through holes. In
another embodiment of the assembly, the circuit board through holes are
replaced with a circuit board opening through which a heat sink structure
passes, the heat sink structure being thermally coupled on one side
thereof to the die cavity lid. The other side of the heat sink structure
engages a metal chassis section which interiorly engages the outer plastic
housing wall of a computer.
| Inventors:
|
Estes; Scott (Austin, TX);
Swamy; Deepak (Austin, TX)
|
| Assignee:
|
Dell USA, L.P. (Austin, TX)
|
| Appl. No.:
|
374320 |
| Filed:
|
January 18, 1995 |
| Current U.S. Class: |
257/712; 257/714; 257/E23.087; 257/E23.104; 257/E23.105; 361/699; 361/719 |
| Intern'l Class: |
H01L 023/34 |
| Field of Search: |
257/712,714,713,715,716
361/699,717,718,719
|
References Cited
U.S. Patent Documents
| 4396936 | Aug., 1983 | McIver et al. | 257/796.
|
| 5270572 | Dec., 1993 | Nakajima et al. | 257/714.
|
| 5305184 | Apr., 1994 | Andresen et al. | 257/714.
|
| 5373417 | Dec., 1994 | Barrett | 257/714.
|
| 5448108 | Sep., 1995 | Quon et al. | 257/714.
|
| 5455458 | Oct., 1995 | Quon et al. | 257/714.
|
Primary Examiner: Crane; Sara W.
Assistant Examiner: Ostrowski; David
Attorney, Agent or Firm: Haynes and Boone, L.L.P.
Claims
What is claimed is:
1. Electronic apparatus comprising:
a circuit board having first and second opposite sides;
an IC package mounted on said first side of said circuit board and
including:
a body portion having a first side facing said first side of said circuit
board and having an opening, an opposite second side, and a cavity
extending from said opening through said body portion toward said second
side thereof,
a heat generating die operatively mounted in said cavity and spaced apart
from said opening toward said second side of said body portion,
a lid member sealingly received in said opening, and
a thermally conductive liquid disposed within and filling said cavity and
serving to conduct die heat therethrough to said lid member; and
heat dissipation means, thermally coupled to said lid member and extending
therefrom through said circuit board, for conducting die heat from said
body portion through said circuit board toward said second side thereof.
2. The electronic apparatus of claim 1 wherein said thermally conductive
liquid is chemically inert.
3. The electronic apparatus of claim 1 wherein said thermally conductive
liquid is electrically insulative.
4. The electronic apparatus of claim 1 wherein said thermally conductive
liquid has a relatively low coefficient of thermal expansion.
5. The electronic apparatus of claim 1 wherein said thermally conductive
liquid is chemically inert, is electrically insulative, and has a
relatively low coefficient of thermal expansion.
6. The electronic apparatus of claim 5 wherein said thermally conductive
liquid is an inert fluorocarbon-based liquid.
7. The electronic apparatus of claim 5 wherein said thermally conductive
liquid is a vacuum pump liquid.
8. The electronic apparatus of claim 1 wherein:
said circuit board has a metal ground plane structure disposed between said
first and second opposite sides thereof, and
said heat dissipation means engage said metal ground plane structure and
are operative to transfer die heat thereto.
9. The electronic apparatus of claim 8 wherein said heat dissipation means
include:
a spaced series of through holes extending between said first and second
opposite sides of said circuit board and having metal linings thermally
interconnected between said lid member and said metal ground plane
structure.
10. The electronic apparatus of claim 9 wherein:
the metal linings of said through holes are thermally connected to said lid
member by a heat spreader plate interposed between the metal linings and
said lid member, and the metal linings of said through holes directly
engage said metal ground plane structure.
11. The electronic apparatus of claim 9 further comprising:
heat sink means secured to said second side of said circuit board and
operative to receive die heat from the metal linings of said through
holes.
12. The electronic apparatus of claim 1 further comprising:
heat sink means, disposed on said second side of said body portion, for
receiving die heat conducted through said body portion said second side
thereof.
13. The electronic apparatus of claim 1 further comprising:
sensing means disposed in said cavity and operative to output a control
signal indicative of a temperature of said thermally conductive liquid in
excess of a predetermined maximum temperature thereof.
14. The electronic apparatus of claim 13 wherein:
said sensing means include a pressure transducer.
15. The electronic apparatus of claim 1 wherein said heat dissipation means
include:
an opening extending through said circuit board between said first and
second opposite sides thereof and generally aligned with said lid member,
and
heat sink means, thermally connected to said lid member and extending
through said circuit board opening, for receiving and dissipating die
heat.
16. The electronic apparatus of claim 15 wherein:
said electronic apparatus further comprises a plastic computer housing wall
having an inner side surface spaced apart from and facing said second side
wall of said circuit board, and a metal chassis structure engaging said
inner side surface, and
said heat sink means are in thermally conductive engagement with said metal
chassis structure.
17. The Electronic apparatus of claim 1 wherein said thermally conductive
liquid is a vacuum pump fluid.
Description
BACKGROUND OF THE INVENTION
The present invention generally relates to circuit board apparatus, and
more particularly relates to apparatus and methods for cooling of
integrated circuit (IC) packages mounted on circuit boards.
Under the conventional method by which integrated circuits are hermetically
packaged, an internal cavity is formed within a multi-tiered substrate
structure, typically of a ceramic material, and opens outwardly through a
bottom side of the substrate structure. A die is then mounted on an upper
side surface portion of the cavity and wire bonded to the various
circuitry tiers of the substrate structure. After the die is operatively
mounted in the cavity, the cavity is filled with an inert gas, such as
nitrogen, and hermetically sealed using a lid member received in the
bottom side cavity opening of the substrate structure. The completed IC
package is then mounted, lid side down, on a side of a circuit board and
appropriately connected to the board circuitry, for example by pins
mounted on the substrate structure and inserted into corresponding holes
in the circuit board.
Since the ceramic material of the IC package substrate structure has a
considerably higher thermal conductivity than the inert gas within the die
cavity, most of the die operational heat conducted outwardly through the
balance of the IC package is conducted upwardly through the substrate
portion directly above the die--only a relatively small amount of heat is
conducted downwardly through the IC package. To facilitate the removal of
this upwardly conducted heat, it is customary to mount a heat sink device
on the top side of the IC package substrate. Typically, these heat sinks
must be provided with large surface areas and accordingly undesirably
impose constraints on already complex system cooling problems--for example
within a computer housing in which the IC package/circuit board structure
is mounted.
As can readily be seen from the foregoing, it would be highly desirable to
provide improved apparatus and methods for more effectively removing
operational heat from an IC package mounted on a side of a circuit board.
It is accordingly an object of the present invention to provide such
improved heat removal apparatus and methods.
SUMMARY OF THE INVENTION
In carrying out principles of the present invention, in accordance with a
preferred embodiment thereof, electronic apparatus is provided in the form
of a circuit board having first and second opposite sides, and an
integrated circuit (IC) package mounted on the first circuit board side.
The IC package includes a body portion having a first side facing the
first circuit board side and having an opening, an opposite second side,
and a cavity extending from the opening through the body portion toward
its second side. A heat generating die is operatively mounted in the
cavity and is spaced apart from the body portion opening toward the second
side of the body portion. A lid member is sealingly received in the body
portion opening.
In accordance with a key aspect of the present invention relative to the IC
package, a thermally conductive liquid is disposed within and fills the
cavity and serves to conduct die heat therethrough to the lid member.
Preferably, the liquid has the further physical characteristics of being
chemically inert, electrically insulative and having a relatively low
coefficient of thermal expansion. Representatively, the liquid may be an
inert fluorocarbon-based liquid or an inert vacuum pump fluid.
Because of the unique use of a thermally conductive liquid in the die
cavity, as opposed to the conventional use of an inert gas such as
nitrogen or highly purified air, a substantial portion of the operational
die heat is transferred to the lid member. To facilitate the removal of
this heat, heat dissipation means are thermally coupled to the lid member,
extend therefrom through the circuit board, and are operative to conduct
die heat from the second body portion side through the circuit board
toward its second side.
In one representative form thereof, the heat dissipation means include a
spaced series of metal-plated through holes extending through the circuit
board, with the metal plating portions of the through holes engaging an
interior ground plane structure within the circuit board and being
thermally coupled to the IC package lid member. Accordingly, a portion of
the operational die heat conducted to the interior ground plane structure
of the circuit board. Die heat dissipation may be augmented by the
securement of a heat sink structure to the second side of the IC package
body portion and/or the securement of a heat sink structure to the second
side of the circuit board in thermal communication with the metal plating
portions of the through holes therein.
In another representative form thereof, the heat dissipation means include,
in place of the plated through holes, an opening formed in the circuit
board in general alignment with the lid member, and a heat sink structure
thermally coupled on one side thereof to the lid member and extending
through the circuit board opening. The opposite side of this heat sink
structure may be thermally coupled to a metal chassis section that
interiorly engages the outer plastic housing wall of a computer.
According to another feature of the invention, sensing means are disposed
within the die cavity and are operative to output a control signal
indicative of die cavity liquid temperature higher than a predetermined
maximum temperature. This control signal may be utilized to automatically
trigger a corrective cooling action such as, for example, the energization
of an appropriate system cooling fan. In a preferred embodiment thereof,
the sensing means include a pressure transducer disposed within the die
cavity liquid.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified schematic cross-sectional view through a
representative circuit board having mounted thereon an integrated circuit
(IC) package provided with improved operational cooling using apparatus
and methods embodying principles of the present invention; and
FIG. 2 is a simplified schematic cross-sectional view through an alternate
embodiment of the circuit board/IC package assembly shown in FIG. 1.
DETAILED DESCRIPTION
Cross-sectionally illustrated in somewhat schematic form in FIG. 1 is an
improved circuit board assembly 10 that embodies principles of the present
invention and includes a specially designed integrated circuit (IC)
package 12 operatively mounted on the top side 14 of a circuit board 16
having a bottom side 18 parallel to the top side 14, and a vertically
spaced pair of interior metal ground planes 20 and 22 parallel to sides 16
and 18 and interdigitated with various interior circuitry tiers 24, 26 and
28.
The IC package 12 has a generally rectangular dielectric body 30 which is
preferably formed from a ceramic or plastic material and has top and
bottom sides 32,34 and a vertically spaced series of interior circuitry
tiers 36,38,40 and 42. Centrally disposed within the IC package body 30 is
a cavity 44 that has an upper side surface 46 and an opening 48 disposed
in the bottom side 34 of the body 30. The die cavity opening 48 is covered
by a metal lid member 50 received and hermetically sealed within the
opening 48. A die 52 is suitably secured to the upper cavity side surface
46 and is wire-bonded in a conventional manner, as at 54, to the body
circuitry tiers 36,38,40,42.
Outwardly circumscribing the die cavity opening 48 are a series of
connector pins 56 that project downwardly from the bottom side 34 of the
IC package body 30 and are received in corresponding openings in the
circuit board 16. In a conventional manner, the pins 56 electrically
couple the circuitry of the die 52 to the circuit board tiers 24,26,28 via
the wire bonds 54 and the IC body circuitry tiers 36,38,40 and 42. For
purposes later described, the circuit board has formed therein a spaced
series of metal-plated through holes 58 disposed generally beneath the die
cavity lid 50 and outwardly circumscribed by the pins 56. The metal
plating of each of the through holes 58 is in direct contact with each of
the metal ground planes 20,22 within the interior of the circuit board 16.
According to a key aspect of the present invention, in contrast to
conventional IC package construction techniques the die cavity 44 is not
filled with an inert gas such as nitrogen or highly purified air. Instead,
the die cavity 44 is filled with a liquid 60 that (1) is thermally
conductive, (2) is chemically inert, (3) is electrically insulative, and
(4) has a low coefficient of thermal expansion. A preferred liquid having
these characteristics is an inert fluorocarbon-based liquid manufactured
under the trade name "Fluorinert" by the 3M Manufacturing Company. Another
suitable liquid having these characteristics is a vacuum pump liquid such
as that manufactured under the trade name "Crytox" by the DuPont Company.
In a conventional IC package whose die cavity is filled with nitrogen,
highly purified air, or another inert gas, the solid IC package body
portion directly above the die has a considerably higher thermal
conductivity than the inert gas within the die cavity does. Accordingly,
only a rather negligible portion of the total die heat transferred to the
IC package body is downwardly transmitted toward the circuit board upon
which the IC package is mounted--most of the die heat passing through the
IC package body is transmitted upwardly to a central portion of its top
side directly above the die.
In the present invention, however, due to the greatly increased thermal
conductivity of the liquid 60, a much larger portion of the operational
die heat is conducted downwardly through the liquid 60 to the metal lid
50. To facilitate the dissipation of this downwardly conducted die heat, a
metal heat spreader plate 62 is suitably secured to the bottom side 34 of
the IC package body 30, with the metal die cavity lid 50 being in direct
thermal engagement with a central top side portion of the plate 62. The
bottom side of the plate 62 is placed in efficient thermal contact with
the top ends of the metal-plated circuit board through holes 58 by a layer
of electrically and thermally conductive adhesive material 64.
Due to this thermal coupling of the bottom side of the IC package body 30
to the top ends of the metal-plated through holes 58, and the
substantially increased thermal conductivity of the die cavity liquid 60,
a substantial portion of the operational heat generated by the die 52 is
transmitted to the metal plating portions of the through holes 58, and
then from such metal plating portions to the metal ground planes 20 and 22
within the interior of the circuit board 16. This unique use of the ground
planes 20,22 as heat dissipation means can advantageously disperse several
watts of operational die heat. Additionally, due to the fact that a
secondary ground path is established by virtue of the plated through holes
58, the overall system is quieter from the standpoint of radiated
emissions.
Of course, a reduced amount of operational die heat will still be conducted
upwardly through the dielectric body 30 to its top side 32--primarily
through a dielectric body portion directly above the die 52. To dissipate
this heat a metal heat spreader plate 66 is secured to the top side 32 of
the IC package body 30 with a layer of thermally conductive adhesive
material 68, and is additionally secured to the bottom side of a suitable
metal heat sink 70.
Because of the substantially increased downward dissipation of operational
die heat provided by the present invention, the heat sink 70 can be
markedly smaller than typically required for a similarly sized
conventional IC package. If additional dissipation of the downwardly
transferred die heat is needed, an auxiliary bottom side metal heat sink
72 may be secured to the bottom side 18 of the circuit board 16, over the
lower ends of the metal-plated through holes 58, using a layer of
electrically and thermally conductive adhesive material 74. In this
manner, a first portion of the operational die heat downwardly transmitted
to the upper ends of the metal through hole plating is conducted into the
metal ground planes 20 and 22, and a second portion of the operational die
heat downwardly transmitted to the upper ends of the metal through hole
plating is conducted into the auxiliary heat sink 72.
The pressure, and thus the temperature, of the thermally conductive die
cavity liquid 60 is continuously monitored by a small pressure transducer
76 mounted within the die cavity 44 and electrically coupled to one of the
board circuitry tiers 24,26,28 sequentially via an IC body circuitry tier
40, a schematically depicted vertical circuit portion 78, and one of the
connector pins 56a. When it senses a die cavity liquid temperature above a
predetermined maximum level, the transducer 76 outputs a corresponding
electrical signal which may be used to automatically take a
temperature-corrective action such energizing a system cooling fan.
Illustrated in FIG. 2 is an alternate embodiment 10a of the previously
described circuit board assembly 10. The modified circuit board assembly
10a is representatively mounted in a computer housing having a plastic
outer wall portion 80 that upwardly engages a metal chassis section 82
disposed beneath the circuit board assembly 10a.
Circuit board assembly 10a is similar to the previously described assembly
10 with the exception that the heat spreader plate 62 on the bottom side
of the IC package body 30, the metal-plated circuit board through holes
58, and the auxiliary heat sink 72 are eliminated. Provided in place of
the metal-plated through holes 56 is a rectangular opening 84 formed
through the circuit board 16 directly beneath the die cavity lid 50. A
metal heat sink 86 is received within the opening 84, has a bottom side in
thermal engagement with the metal chassis portion 82, and has a top side
coupled to the underside of the die cavity lid 50 by a layer of an
electrically and thermally conductive adhesive material 88. In this
manner, operational die heat transmitted downwardly through the die cavity
liquid 60 is conducted to the outer plastic housing wall 80 sequentially
via the adhesive material 88, the heat sink 86 and the metal chassis
section 82.
The foregoing detailed description is to be clearly understood as being
given by way of illustration and example only, the spirit and scope of the
present invention being limited solely by the appended claims.
Top